SCIENCE || CLASS 09TH || CHAPTER 04 || BASIC CONCEPTS || CBSE AND MP BOARD

  "AKC SCIENCE CLASSES"

CLASS 09 TH (CBSE AND MP BOARD)

CHAPTER 04

STRUCTURE OF THE ATOM

BASIC CONCEPT 

(1) Cathode ray consists of negatively charged particles known as electrons. 

(2) An electron has -1 unit (1.6 ✖ 10⁻¹⁹) C charge and negligible (9.1 ✖ 10⁻³¹ kg) mass.

^{(3) An electron is regarded as universal particle i.e., its charge and mass remain the same.}

^{(4) A proton has +1 unit (1.6 x 10⁻¹⁹) charge and negligible ( 1.67 x 10⁻²⁷ kg) mass.}

^{(5) Thomson's model of an atom is also known as Raisin Pudding Model.}

^{(6) Alpha particles for scattering experiment were obtained from radio active element radium.}

^{(7) Alpha particles are helium nuclei (He²⁺) and have 4u mass and +2 units charge.} 

^{(8) According to Rutherford, the nucleus of the atom contains all the protons.}

^{(9) Chadwick confirmed the presence of neutrons along with protons in the nucleus of an atom.}

^{(10) According to Rutherford, all the electrons are present in the extra nuclear space i.e., the space around the nucleus.}

^{(11) Electrons are called planetary electrons.}

^{(12) According to Bohr's theory, the the different energy shells for the electrons are designated as :-}

        ^{K, L, M, N, O, ....etc.}

^{(13) The order of the energy of the energy shells is :-}

       ^{K < L < M < N < O ..........etc.}

^{(14) Neutrons were discovered by Chadwick in 1931.}

^{(15) Atomic number (Z) of an element is equal to number of protons.}

^{(16) No. of protons and electrons are same in a neutral atom only. These are different in an ion.}

^{(17) The distribution of the electrons in the various energy shells is given by Bohr-Bury scheme.}

^{(18) According to Bohr-Bury scheme, the maximum no. of electrons in any energy shell is given as 2n². The outermost shell cannot have more than 8 electrons.}

^{(19) Valency of an element is the combining capacity of its atoms.}

^{(20) Valency of an element is equal to either the number of valence electrons or eight minus the number of valence electrons.}

^{(21) Elements He, Ne, and Ar are known as inert elements and have zero valency.}

^{(22) Isotopes are the different atoms of the same element having same atomic number and different mass numbers.}

^{(23) Isotopes of an element have same electronic configuration and are also chemically similar.}

^{(24) Radio-isotopes emit powerful radiations known as α-rays, β-rays and ɣ-rays.}

^{(25) Uranium-235 isotopes are the major source of nuclear energy.}

^{(26) The elements which exist as isotopes have generally fractional atomic masses.}

^{(27) Isobars have different atomic numbers but same mass numbers.}

^{(28) Isobars belong to different elements.}

^{(29) Isobars differ in the number of electrons, protons as well as neutrons.} 

^{(30) The elements are identified by their atomic numbers and not by mass numbers.}

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